Seriously though, Dr. Coyne could you point me to some post of yours or some articles that clearly explain the determinist position (I’m not even sure I am describing it accurately here!). ...I have criticized him before, but his conciseness this time shows his errors more clearly.
The best answer I can give (besides reading Sean Carroll’s “The Big Picture”) is to say that our brain is made of matter, and matter follows the laws of physics. Insofar as our neurons could behave fundamentally unpredictably, if affected by quantum mechanics in their firing, that doesn’t give us a basis for agency either.
Since our behaviors all come from our material bodies and brains, which obey the laws of physics, which by and large are deterministic on a macro scale, then our behaviors at any one instant are determined as well by the configuration of molecules in the Universe.
All you have to do is accept that our bodies and brains are made of stuff, and stuff on the macro scale is deterministic in its behavior. Even compatibilists accept these points as well the fundamental determinism (though often unpredictability) of our behavior.
See the book Free Will by Sam Harris which simply explains why we have no basis, in the form of data, to conclude the we can freely make decisions.
Yes, the laws of physics are "by and large ... deterministic on a macro scale". So is human behavior. But macro physics cannot predict with perfect precision, and human behavior also deviates from predictions. So nothing about macro physics contradicts free will.
Neurons certainly are affected by quantum mechanics. Both agency and quantum mechanics lead to unpredictability. So why can't one be related to the other?
Saying that we have "no data" to support freely-made decisions is just nutty. Everyone makes decisions every day. Maybe some of these decisions are illusory somehow, but they are certainly data in favor of decisions.
Free will is mostly a philosophical issue, and you can believe in it or not. I am just rebutting what is supposedly a scientific argument against it.